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Question #40461

Difficulty: 8/10 | 🟢 Free

The Question

Let f(z)=12z3+kz2+czf(z) = 12z^3 + k z^2 + c z, where k,cinmathbbRk, c \\in \\mathbb{R}. A particle moves in the complex plane along the curve z(t)=eitz(t) = e^{it} for tinleft[0,fracπ2right]t \\in \\left[0, \\frac{\pi}{2}\\right]. Let u(t)=textRe(f(z(t)))u(t) = \\text{Re}(f(z(t))) and v(t)=textIm(f(z(t)))v(t) = \\text{Im}(f(z(t))). It is given that v(t)v(t) satisfies the conditions of Rolle's Theorem on the interval left[0,fracπ2right]\\left[0, \\frac{\pi}{2}\\right], and u(t)u(t) has a local extremum at t=arccosleft(frac34right)t = \\arccos\\left(\\frac{3}{4}\\right). If MM and mm are the absolute maximum and absolute minimum values of u(t)u(t) on left[0,fracπ2right]\\left[0, \\frac{\pi}{2}\\right], find the value of 8(M+m)8(M + m).

Options

  • A.

    151

  • B.

    39

  • C.

    153

  • D.

    41

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Monster

Ultra-high difficulty questions designed to test your limit, stamina, and deep conceptual understanding.

Concepts Behind This Question

Algebraic Manipulation of i|Rolle's Theorem Anchors|Parametric Derivative Endpoint Trap|Global Extrema on Intervals

Why This Question Is Tricky

Common Mistakes

This question deploys the 'Parametric Derivative Endpoint Trap'.

Students typically find extrema by setting the derivative u′(t)=0u'(t) = 0, which yields t=0t=0 and t=arccos(3/4)t=\\arccos(3/4).

Testing these gives values of 55 and −1/8-1/8, leading to an incorrect maximum of 55 (Option B).

However, the true absolute maximum occurs at the boundary t=pi/2t=\\pi/2 (where x=cost=0x=\\cos t = 0), yielding 1919.

Because u′(pi/2)=24neq0u'(\\pi/2) = 24 \\neq 0, this endpoint is invisible to the derivative test, punishing students who fail to manually check the boundaries of the parametric interval.

The problem also uses Rolle's Theorem as an algebraic anchor to deduce the hidden coefficient cc.

Quick Facts About This Question

Question Information

SubjectMathematics
ChapterComplex Numbers and Quadratic Equations - Class 11
ConceptAlgebraic Manipulation of i
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree